1. Field of the Invention
The present invention relates to a springy shield element, and more particularly to a flexible shielding element for biasing magnetic tape in a cassette against the tape head while also magnetically shielding the head.
2. Description of the Prior Art
Generally, magnetic heads are protected from magnetic noise fields by protective shields. Customarily, the magnetic heads, with the exception of the tape head against which the magnetic tape rests, are surrounded by a shield. Shielded magnetic heads of this type, either a combined recording and playback head or separate magnetic heads (in the case of commercial compact cassettes for sound recordings, in which the tape is rewound between two wound cores), pass through openings in the frontal face of the cassette when in the operating position. At these locations, shielding elements are disposed within the cassette, commonly in the form of a flat or U-shaped sheet metal consisting of a highly permeable iron-nickel alloy, and are intended to cover the tape head. In order to press the magnetic tape against the magnetic head, additional spring elements are provided at these same locations. In the cassette according to the German utility model No. 72 08 034, a rigid or fixed shield member, which is arranged opposite the magnetic head on the other side of the magnetic tape and which bears a glide support for the magnetic tape is pressed, on its side not facing the magnetic tape, against the magnetic head by means of a spring element. In the case of other commercial cassettes, the contact pressure spring which bears a glide support consisting of felt, or a foam-like material, is disposed between the sound recording tape and the shield element. In addition, from the German AS No. 20 36 754, a shield element is known which is designed in the form of a hollow cuboid which is open on one side and whose four lateral faces overlap the tape head, including the shield surrounding the tape head when in the operating mode. Through this form of shield the influence of the shield material is reduced, so that instead of the highly permeable alloys, particularly the costly iron-nickel alloys, less costly materials of a relatively low permeability, such as soft-magnetic types of iron, can be utilized. In this type of shielding, a separate contact pressure spring for the second recording tape is also necessary.
The combining of the shielding and contact-pressure spring function in a single component is known from the German OS No. 26 33 672. The component there consists of a strip-shaped, two-layer laminate, whereby the one layer consists of a springy material, for example beryllium bronze, and the other layer consists of a stress-free material of high magnetic permeability, for example iron, nickel, or an iron-nickel alloy. Furthermore, there is disposed on the laminate a flexible or elastic contact pressure piece which keeps the springy shield element at a distance of approximately 0.8 to 1 mm from the sound head. By combining the shielding and contact-pressure function in one component, the assembly is considerably simplified and the space requirement for the spring and shield in the cassette is reduced while obtaining the same or even an improved shielding effect. However, the manufacture of the two-layer laminate is comparatively costly.